Recessed single crystalline source and drain for semiconductor-on-insulator devices

ABSTRACT

After formation of a gate stack, regions in which a source and a drain are to be formed are recessed through the top semiconductor layer and into an upper portion of a buried single crystalline rare earth oxide layer of a semiconductor-on-insulator (SOI) substrate so that a source trench and drain trench are formed. An embedded single crystalline semiconductor portion epitaxially aligned to the buried single crystalline rare earth oxide layer is formed in each of the source trench and the drain trench to form a recessed source and a recessed drain, respectively. Protrusion of the recessed source and recessed drain above the bottom surface of a gate dielectric can be minimized to reduce parasitic capacitive coupling with a gate electrode, while providing low source resistance and drain resistance through the increased thickness of the recessed source and recessed drain relative to the thickness of the top semiconductor layer.

BACKGROUND

The present disclosure relates to semiconductor structures, andparticularly to semiconductor structures employing recessed singlecrystalline source and drain embedded in an upper portion of a buriedsingle crystalline rare earth oxide layer of asemiconductor-on-insulator substrate, and methods of manufacturing thesame.

High source resistance or high drain resistance adversely impacts theperformance of a field effect transistor by limiting the on-current ofthe field effect transistor. Thus, devices formed on asemiconductor-on-insulator (SOI) substrate having a thin topsemiconductor layer is prone to performance degradation due to reductionin thickness of the source and the drain. For extremely thinsemiconductor-on-insulator (ETSOI) devices in which the topsemiconductor layer has a thickness less than 30 nm, the problem of highsource resistance and high drain resistance significantly degrades theon-current and the overall performance of the ETSOI devices.

BRIEF SUMMARY

A semiconductor-on-insulator (SOI) substrate including a buried singlecrystalline rare earth oxide layer is provided. The buried singlecrystalline rare earth oxide layer includes a single crystalline layerof an oxide of at least one rare earth element, and has a latticeconstant that is compatible with epitaxial growth of a singlecrystalline semiconductor material thereupon. After formation of a gatestack on the top semiconductor layer of the SOI substrate, regions inwhich a source and a drain are to be formed are recessed through the topsemiconductor layer and into an upper portion of the buried singlecrystalline rare earth oxide layer. A source trench and drain trench areformed by the recessing. An embedded single crystalline semiconductorportion epitaxially aligned to the underlying buried single crystallinerare earth oxide layer is formed in each of the source trench and thedrain trench to form a recessed source region and a recessed drainregion, respectively. Protrusion of the recessed source region andrecessed drain region above the bottom surface of a gate dielectric canbe minimized to reduce parasitic capacitive coupling with a gateelectrode, while providing low source resistance and drain resistancethrough the increased thickness of the recessed source and recesseddrain relative to the thickness of the top semiconductor layer.

According to an aspect of the present disclosure, a semiconductorstructure is provided, which includes: a semiconductor substrateincluding a buried single crystalline rare earth oxide layer including atrench, the trench having a recessed surface that is recessed relativeto a topmost surface of the buried single crystalline rare earth oxidelayer and having sidewalls extending from the topmost surface to therecessed surface, a single crystalline semiconductor material regionhaving a bottommost surface that is in contact with the topmost surfaceof the buried single crystalline rare earth oxide layer; and an embeddedsingle crystalline semiconductor material region filling the trench,wherein a portion of the embedded single crystalline semiconductormaterial region is epitaxially aligned to a crystal structure of theburied single crystalline rare earth oxide layer, laterally contacts thesingle crystalline semiconductor material region.

According to another aspect of the present disclosure, a method offorming a semiconductor structure is provided, which includes: formingat least one trench through a top semiconductor layer and into an upperportion of a buried single crystalline rare earth oxide layer in asemiconductor substrate; and forming at least one embedded singlecrystalline semiconductor material region by filling each of the atleast one trench with a single crystalline semiconductor material regionthat includes a portion that is epitaxially aligned to a crystalstructure of the buried single crystalline rare earth oxide layer. Eachof the at least one embedded single crystalline semiconductor materialregion laterally contacts a single crystalline semiconductor materialregion located within the top semiconductor layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is vertical cross-sectional view of a first exemplarysemiconductor structure after formation of shallow trench isolationstructures in a semiconductor-on-insulator (SOI) substrate including aburied single crystalline rare earth oxide layer according to a firstembodiment of the present disclosure.

FIG. 1B is a top-down view of the first exemplary semiconductorstructure of FIG. 1A.

FIG. 2A is vertical cross-sectional view of the first exemplarysemiconductor structure after formation of a gate stack, dummy gatestacks, a gate spacer, and dummy gate spacers according to the firstembodiment of the present disclosure.

FIG. 2B is a top-down view of the first exemplary semiconductorstructure of FIG. 2A.

FIG. 3A is a vertical cross-sectional view of the first exemplarysemiconductor structure after forming a source trench and a drain trenchby etching portions of a top semiconductor layer and an upper portion ofthe buried single crystalline rare earth oxide layer that are notcovered by the combination of the gate stack, the dummy gate stacks, thegate spacer, the dummy gate spacers, and a patterned photoresistaccording to the first embodiment of the present disclosure.

FIG. 3B is a top-down view of the first exemplary semiconductorstructure of FIG. 3A.

FIG. 4A is a vertical cross-sectional view of the first exemplarysemiconductor structure after removing the overlying polycrystallinesemiconductor layer and portions of the embedded epitaxial semiconductorportions above the topmost surface of the top semiconductor layeraccording to the first embodiment of the present disclosure.

FIG. 4B is a top-down view of the first exemplary semiconductorstructure of FIG. 4A.

FIG. 5A is a vertical cross-sectional view of the first exemplarysemiconductor structure after formation of contact structures andinterconnect line structures according to the first embodiment of thepresent disclosure.

FIG. 5B is a top-down view of the first exemplary semiconductorstructure of FIG. 5A.

FIG. 6A is vertical cross-sectional view of a second exemplarysemiconductor structure after formation of a gate stack and a gatespacer according to the second embodiment of the present disclosure.

FIG. 6B is a top-down view of the second exemplary semiconductorstructure of FIG. 6A.

FIG. 7A is a vertical cross-sectional view of the second exemplarysemiconductor structure after forming a source trench and a drain trenchby etching portions of a top semiconductor layer and an upper portion ofthe buried single crystalline rare earth oxide layer that are notcovered by the combination of the gate stack, the gate spacer, and apatterned photoresist according to the second embodiment of the presentdisclosure.

FIG. 7B is a top-down view of the second exemplary semiconductorstructure of FIG. 7A.

FIG. 8A is a vertical cross-sectional view of the second exemplarysemiconductor structure after epitaxial growth of embedded singlecrystalline semiconductor portions on the recessed surfaces of theburied single crystalline rare earth oxide layer to form a recessedsource region and a recessed drain region according to the secondembodiment of the present disclosure.

FIG. 8B is a top-down view of the second exemplary semiconductorstructure of FIG. 8A.

FIG. 9A is a vertical cross-sectional view of the second exemplarysemiconductor structure after formation of contact structures andinterconnect line structures according to the second embodiment of thepresent disclosure.

FIG. 9B is a top-down view of the second exemplary semiconductorstructure of FIG. 9A.

DETAILED DESCRIPTION

As stated above, the present disclosure relates to semiconductorstructures employing recessed single crystalline source and drainembedded in an upper portion of a buried single crystalline rare earthoxide layer of a semiconductor-on-insulator substrate, and methods ofmanufacturing the same, which are now described in detail withaccompanying figures. Like and corresponding elements mentioned hereinand illustrated in the drawings are referred to by like referencenumerals. The drawings are not necessarily drawn to scale.

Referring to FIGS. 1A and 1B, a first exemplary semiconductor structureaccording to a first embodiment of the present disclosure includes asemiconductor-on-insulator (SOI) substrate 8. The SOI substrate 8includes a stack, from bottom to top, of a handle substrate 10, a buriedsingle crystalline rare earth oxide layer 20, and a top semiconductorlayer 30.

The handle substrate 10 provides structural support to, and preventsdeformation or breakage of, the buried single crystalline rare earthoxide layer 20 and the top semiconductor layer 30. The thickness of thehandle substrate 10 can be from 50 microns to 2 mm, although lesser andgreater thicknesses can also be employed. The handle substrate 10 caninclude an amorphous, polycrystalline, or single crystallinesemiconductor material, an insulator material, a conductor material, ora stack thereof.

The buried single crystalline rare earth oxide layer 20 includes asingle crystalline rare earth oxide material. Method of forming a singlecrystalline rare oxide material is described, for example, in U.S. Pat.Nos. 7,655,327 and 7,709,826 to Atanackovic.

Rare earth elements are also referred to as Lanthanides, and include La,Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The ionicradii of rare earth elements decrease gradually with the atomic number,and the total variation of the ionic radii of rare earth elements isless than 15% among one another. The rare earth elements form varioussingle crystalline dielectric oxides with a valance of +3, i.e., adielectric oxide having a chemical formula of M₂O₃, in which M can beany of the rare earth elements.

Crystalline rare earth oxides are lattice coincident on a class ofelemental or alloyed single crystalline semiconductor materialsincluding single crystalline silicon, a single crystallinesilicon-germanium alloy, a single crystalline silicon-carbon alloy, anda single crystalline silicon-germanium-carbon alloy. For each singlecrystalline M₂O₃ in which M is a rare earth element, at least one singlecrystalline semiconductor material having a lattice constant that is onehalf the lattice constant of the single crystalline M₂O₃ exists amongsingle crystalline silicon, a single crystalline silicon-germaniumalloy, a single crystalline silicon-carbon alloy, and a singlecrystalline silicon-germanium-carbon alloy.

For example, twice the lattice constant of silicon is between thelattice constant of gadolinium oxide (Gd₂O₃) and the lattice constant ofneodymium oxide (Nd₂O₃). Thus, the composition of a single crystallinealloy of gadolinium oxide and neodymium oxide can be selected to matchtwice the lattice constant of silicon. In other words, the value x inthe compound Gd_(2-x)Nd_(x)O₃ can be selected to provide a singlecrystalline compound having a lattice constant that is twice the latticeconstant of silicon.

In another example, twice the lattice constant of germanium is betweenthe lattice constant of praseodymium oxide (Pd₂O₃) and the latticeconstant of lanthanum oxide (La₂O₃). Thus, the composition of a singlecrystalline alloy of praseodymium oxide and lanthanum oxide can beselected to match twice the lattice constant of germanium. In otherwords, the value y in the compound Pd_(2-y)La_(y)O₃ can be selected toprovide a single crystalline compound having a lattice constant that istwice the lattice constant of silicon.

In a non-limiting exemplary embodiment, the buried single crystallinerare earth oxide layer 20 can include a single crystalline rare earthoxide selected from Er₂O₃, Gd₂O₃, Nd₂O₃, Pr₂O₃, La₂O₃, and a singlecrystalline alloy thereof.

In addition, crystalline rare earth oxides are lattice coincident onvarious single crystalline semiconductor materials that include III-Vcompound semiconductor materials and II VI compound semiconductormaterials. Thus, for each single crystalline M₂O₃ in which M is a rareearth element, at least one single crystalline compound semiconductormaterial having a lattice constant that is one half the lattice constantof the single crystalline M₂O₃ exists.

The thickness of the buried single crystalline rare earth oxide layer 20can be from 25 nm to 300 nm, although lesser and greater thicknesses canalso be employed. In one embodiment, the thickness of the buried singlecrystalline rare earth oxide layer 20 can be from 50 nm to 150 nm.

The top semiconductor layer 30 includes a single crystallinesemiconductor material. The single crystalline semiconductor material ofthe top semiconductor layer 30 can be selected from, but is not limitedto, silicon, a silicon germanium alloy, a silicon carbon alloy, asilicon germanium carbon ally, a III-V compound semiconductor material,a II-VI compound semiconductor material, and an alloy or a combinationthereof.

The thickness of the top semiconductor layer 30 can be from 3 nm to 200nm, although lesser and greater thicknesses can also be employed. In oneembodiment, the SOI substrate 8 is an extremely thinsemiconductor-on-insulator having a thickness from 3 nm to 15 nm.

The stack of the handle substrate 10, the buried single crystallinesemiconductor layer, and the top semiconductor layer 30 can be formed,for example, by providing a semiconductor substrate including a singlecrystalline semiconductor layer having a same composition as the topsemiconductor layer 30, forming a hydrogen-implanted layer in the singlecrystalline semiconductor layer at a depth equal to a desired thicknessfor the top semiconductor layer 30, depositing or bonding a layer of asingle crystalline rare earth oxide material having a same thickness asa desired thickness for the top semiconductor layer 30, bonding thesubstrate including the hydrogen-implanted layer and the layer of thesingle crystalline rare earth oxide material to the handle substrate 10,and separating the bonded substrate along the hydrogen-implanted layer.Thus, the single crystalline semiconductor layer having the samecomposition as the top semiconductor layer 30 is incorporated as the topsemiconductor layer 30 into the SOI substrate 8, and the layer of thesingle crystalline rare earth oxide material is incorporated into theSOI substrate 8 as the buried single crystalline rare earth oxide layer20.

In one embodiment, prior to bonding with the handle substrate 8, thelayer of the single crystalline rare earth oxide material that issubsequently incorporated the SOI substrate 8 can be formed withepitaxial alignment to the single crystalline semiconductor layer thatis incorporated as the top semiconductor layer 30 into the SOI substrate8. For example, the layer of the single crystalline rare earth oxidematerial can be formed by epitaxy of the single crystalline rare earthoxide material directly on the semiconductor surface of the singlecrystalline semiconductor layer. In this embodiment, the singlecrystalline semiconductor material of the top semiconductor layer 10 isin epitaxial alignment with the single crystalline insulator material ofthe buried single crystalline rare earth oxide layer 20.

In another embodiment, prior to bonding with the handle substrate 8, thelayer of the single crystalline rare earth oxide material that issubsequently incorporated the SOI substrate 8 can be formed withoutepitaxial alignment to the single crystalline semiconductor layer thatis incorporated as the top semiconductor layer 30 into the SOI substrate8. For example, the layer of the single crystalline rare earth oxidematerial can be formed by bonding the layer of the single crystallinerare earth oxide material directly on the semiconductor surface of thesingle crystalline semiconductor layer. In this embodiment, the singlecrystalline semiconductor material of the top semiconductor layer 10 isnot in epitaxial alignment with the single crystalline insulatormaterial of the buried single crystalline rare earth oxide layer 20.

A shallow trench isolation structure 22 can be formed in the topsemiconductor layer 30 by forming a shallow trench extending from thetop surface of the top semiconductor layer 30 at least to the bottomsurface of the top semiconductor layer 30, and subsequently filling theshallow trench with a dielectric material such as silicon oxide, siliconnitride, and/or silicon oxynitride. Excess dielectric material above thetop surface of the top semiconductor layer 30 is removed, for example,by planarization such as chemical mechanical planarization (CMP).

The shallow trench isolation structure 22 can laterally surround, andelectrically isolate, a contiguous single crystalline semiconductormaterial region 32′ from other single crystalline semiconductor materialregions 36 located within the top semiconductor layer 30. In otherwords, the contiguous single crystalline semiconductor material region32′ can be laterally spaced from the other single crystallinesemiconductor material regions 36 by the shallow trench isolationstructure 22.

The contiguous single crystalline semiconductor material region 32′ hasa bottommost surface that is in contact with the topmost surface of theburied single crystalline rare earth oxide layer 20. The shallow trenchisolation structure 22 contacts the topmost surface of the buried singlecrystalline rare earth oxide layer 20 and laterally surrounds thecontiguous single crystalline semiconductor material region 32′.

Referring to FIGS. 2A and 2B, a gate dielectric layer, a gate conductorlayer, and a gate cap dielectric layer are sequentially deposited andlithographically patterned to form a gate stack and at least one dummygate stack. The gate stack includes a gate dielectric 50, a gateelectrode 52, and a gate cap dielectric 58. Each of the at least onedummy gate stack includes a dummy gate dielectric 51,a dummy gateelectrode 53, and a dummy gate cap dielectric 59.

Specifically, the gate dielectric layer can include a siliconoxide-based gate dielectric material, which can be, for example, siliconoxide, silicon oxynitride, or a dielectric stack including siliconnitride and at least one of silicon oxide and silicon oxynitride.Additionally or alternatively, the gate dielectric layer can include ahigh dielectric constant (high-k) material layer having a dielectricconstant greater than 8.0. Exemplary dielectric materials having adielectric constant greater than 8.0 include a dielectric metal oxide,which is a high-k material containing a metal and oxygen, and is knownin the art as high-k gate dielectric materials. Dielectric metal oxidescan be deposited by methods well known in the art including, forexample, chemical vapor deposition (CVD), physical vapor deposition(PVD), molecular beam deposition (MBD), pulsed laser deposition (PLD),liquid source misted chemical deposition (LSMCD), atomic layerdeposition (ALD), etc. Exemplary high-k dielectric material includeHfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃, HfO_(x)N_(y),ZrO_(x)N_(y), La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y),SrTiO_(x)N_(y), LaAlO_(x)N_(y), Y₂O_(x)N_(y), a silicate thereof, and analloy thereof. Each value of x is independently from 0.5 to 3 and eachvalue of y is independently from 0 to 2. The thickness of the gatedielectric layer can be from 0.9 nm to 6 nm, and preferably from 1.0 nmto 3 nm. The gate dielectric layer may have an effective oxide thicknesson the order of or less than 1 nm.

The gate conductor layer includes at least one conductive material. Theat least one conductive material can include a doped semiconductormaterial and/or a metallic material. The doped semiconductor materialmay be deposited as an intrinsic semiconductor material and subsequentlydoped by implantation of electrical dopants such as B, Ga, In, P, As,and/or Sb, or can be in-situ doped during deposition. The dopedsemiconductor material can be deposited as an amorphous material and isconverted into a polycrystalline material in subsequent high temperatureprocessing steps, or can be deposited as a polycrystalline material. Themetallic material may, or may not, include at least one work functionmetallic material that is employed to adjust the threshold voltage of afield effect transistor to be subsequently formed. The metallic materialcan include a high-conductivity metallic material such as W, Al, and/oralloys thereof. The material(s) of the gate conductor layer can bedeposited by methods well known in the art including, for example,chemical vapor deposition (CVD), physical vapor deposition (PVD), atomiclayer deposition (ALD), etc. The thickness of the gate conductor layeras deposited can be the same as the target thickness for a gateelectrode to be subsequently formed, and can be from 30 nm to 300 nm,although lesser and greater thicknesses can also be employed.

The gate cap dielectric layer includes a dielectric material such assilicon oxide, silicon nitride, or silicon oxynitride. The gate capdielectric layer can be deposited, for example, by chemical vapordeposition. The thickness of the gate cap dielectric layer can be from10 nm to 60 nm, although lesser and greater thicknesses can also beemployed.

The stack of the gate dielectric layer and the gate conductor layer issubsequently patterned, for example, by applying a photoresistthereupon, lithographically patterning the photoresist, and transferringthe pattern in the photoresist into the underlying stack of the gateconductor layer and the gate dielectric layer employing an anisotropicetch that uses the patterned photoresist as an etch mask. The topsemiconductor layer 30 can be the etch stop layer for the anisotropicetch. Remaining portions of the gate cap dielectric layer after theanisotropic etch include the gate cap dielectric 58 and the at least onedummy gate cap dielectric 59. Remaining portions of the gate conductorlayer after the anisotropic etch include the gate electrode 52 and theat least one dummy gate electrode 53. Remaining portions of the gatedielectric layer after the anisotropic etch include the gate dielectric50 and the at least one dummy gate dielectric 51.

At least one contact via structure (See FIGS. 5A and 5B) is subsequentlyformed on the gate electrode 52 so that the gate electrode 52 can beelectrically biased during the operation of a field effect transistor tobe formed. The gate dielectric 50 underlies the gate electrode 52. Theat least one dummy gate electrode 53 is not contacted by a contact viastructure in subsequent processing steps. Each of the at least one dummygate dielectric 51 underlies one of the at least one dummy gateelectrode 53. The gate dielectric 50 and the at least one dummy gatedielectric 51 include the same material(s) and have the same thickness.The gate electrode 52 and the at least one dummy gate electrode 52include the same material(s) and have the same thickness.

Optionally, the portions of the contiguous single crystallinesemiconductor material region 32′ that are not covered by the gate stack(50, 52) or the at least one dummy gate stack (51, 53) can be doped byion implantation of electrical dopants such as B, Ga, In, P, As, and/orSb to form source and drain extension regions. Alternatively, thecontiguous single crystalline semiconductor material region 32′ canremain undoped, or can have the same type and concentration ofelectrical dopants as originally provided at the time of formation ofthe SOI substrate 8 prior to formation of the shallow trench isolationstructure 22.

The gate stack (50, 52) can straddle over a middle portion of thecontiguous single crystalline semiconductor material region 32′. Each ofthe at least one dummy gate stack (51, 53) can overlie an interfacebetween the shallow trench isolation structure 22 and the contiguoussingle crystalline semiconductor material region 32′.

A dielectric material layer can be conformally deposited on the topsurface of the top semiconductor layer 30 and exposed surfaces of thegate stack (50, 52) and the at least one dummy gate stack (52, 53). Thedielectric material layer is anisotropically etched by an anisotropicetch, which can be, for example, a reactive ion etch. Horizontalportions of the dielectric material layer are removed by the anisotropicetch. Remaining vertical portions of the dielectric material layerlaterally contact the sidewalls of, and laterally encloses, each of thegate stack (50, 52) and the at least one dummy gate stack (51, 53). Theremaining portions of the dielectric material layer that contact thesidewalls of the gate stack (50, 52) constitute gate spacers 56. Theremaining portions of the dielectric material layer that contact thesidewalls of each of the at least one dummy gate stack (51, 53)constitute at least one dummy gate spacer 57.

Referring to FIGS. 3A and 3B, a photoresist 77 is applied over the SOIsubstrate 8, the gate stack (50, 52), the at least one dummy gate stack(51, 53), the gate spacer 56, and the at least one dummy gate spacer 57.The photoresist 77 is lithographically patterned so that a first area ofthe SOI substrate 8 is not covered by the photoresist 77 after exposureand development on one side (which is herein referred to as a“source-side”) of the gate stack (50, 52), and a second area of the SOIsubstrate 8 is not covered by the photoresist 77 after exposure anddevelopment on the opposite side (which is herein referred to as a“drain-side”) of the gate stack (50, 52).

The photoresist 77 can be lithographically patterned to have an edgethat overlies a dummy gate stack (51, 53) located on a source side,i.e., a source-side dummy gate stack (51, 53), and another edge thatoverlies a dummy gate stack (51, 53) located on a drain side, i.e., adrain-side dummy gate stack (51, 53). In one embodiment, a physicallyexposed source-side area of the contiguous single crystallinesemiconductor material region 32′ can be laterally bounded by an outersidewall of the gate spacer 56 and an outer sidewall of one of the atleast one dummy gate spacer 57. A physically exposed drain-side area ofthe contiguous single crystalline semiconductor material region 32′ canbe laterally bounded by another outer sidewall of the gate spacer 56 andan outer sidewall of another of the at least one dummy gate spacer 57.

An anisotropic etch is performed employing the combination of thephotoresist 77, the gate stack (50, 52), the at least one dummy gatestack (51, 53), the gate spacer 56, and the at least one dummy gatespacer 57 as an etch mask. A source trench 24 is formed by removing anentirety of the contiguous single crystalline semiconductor materialregion 32′ and an upper portion of the buried single crystalline rareearth oxide layer 20 that are located on the source side and notprotected by the etch mask including that combination of the photoresist77, the gate stack (50, 52), the at least one dummy gate stack (51, 53),the gate spacer 56, and the at least one dummy gate spacer 57. A draintrench 26 is formed by removing an entirety of the contiguous singlecrystalline semiconductor material region 32′ and an upper portion ofthe buried single crystalline rare earth oxide layer 20 that are locatedon the drain side and not protected by the etch mask including thatcombination of the photoresist 77, the gate stack (50, 52), the at leastone dummy gate stack (51, 53), the gate spacer 56, and the at least onedummy gate spacer 57.

Thus, each of the source trench 24 and the drain trench 26 is formedthrough the top semiconductor layer 30 and into an upper portion of theburied single crystalline rare earth oxide layer 20. Each of the sourcetrench 24 and the drain trench 26 has a trench bottom surface, which isa recessed horizontal surface that is recessed relative to a topmostsurface of the buried single crystalline rare earth oxide layer 20. Eachof the source trench 24 and the drain trench 26 has sidewalls extendingfrom the topmost surface of the buried single crystalline rare earthoxide layer 20 to the recessed horizontal surface. The recessedhorizontal surface, i.e., the bottom surface, of the source trench 24can be coplanar with the recessed horizontal surface of the drain trench26.

One sidewall of the source trench 24 is vertically coincident, i.e.,coincide in a top down view in a vertical direction (which is thedirection perpendicular to the topmost surface of the top semiconductorlayer 30), with an outer sidewall of the gate spacer 56 that is locatedon the source side. Another sidewall of the source trench 24 can bevertically coincident with an outer sidewall of a dummy gate spacer 57located on the source side. One sidewall of the drain trench 26 isvertically coincident with an outer sidewall of the gate spacer 56 thatis located on the drain side. Another sidewall of the drain trench 26can be vertically coincident with an outer sidewall of a dummy gatespacer 57 located on the drain side.

The remaining portion of the contiguous single crystalline semiconductormaterial region 32′ underlying the gate stack (50, 52) and the gatespacer 56 and located between the source trench 24 and the drain trench26 is herein referred to as a first single crystalline semiconductormaterial region 32. The at least one remaining portion of the contiguoussingle crystalline semiconductor material region 32′ that underlie theat least one dummy gate stack (51, 53) and the at least one dummy gatespacer 57 and is located farther away laterally from the gate stack (50,52) than the source trench 24 or the drain trench 26 is herein referredto as at least one second single crystalline semiconductor materialportion 31. The at least one second single crystalline semiconductormaterial portion 31 laterally contacts the shallow trench isolationstructure 22.

Referring to FIGS. 4A and 4B, a semiconductor material is selectivelydeposited within the source trench 24 and with the drain trench 26. Thedeposition of the semiconductor material can be effected, for example,by a selective epitaxy process. During the selective deposition of thesemiconductor material, the semiconductor material is deposited onsemiconductor surfaces, and is not deposited on dielectric surfaces suchas the surfaces of the gate spacers 56, the gate cap dielectric 58, theat least one dummy gate cap dielectric 59, and the shallow trenchisolation structure 22. A single crystalline semiconductor material isdeposited on exposed single crystalline surfaces of the buried singlecrystalline rare earth oxide layer 20 and exposed single crystallinesurfaces of the first single crystalline semiconductor material region32 and the at least one second single crystalline semiconductor materialportion 31. Specifically, the single crystalline semiconductor materialis deposited on the entirety of the sidewalls of the source trench 24,the entirety of the sidewalls of the drain trench 26, the entirety ofthe bottom surface of the source trench 24, and the entirety of thebottom surface of the drain trench 26.

In a selective semiconductor material deposition process, an etchant gassuch as HCl is flowed into a processing chamber concurrently with, oralternately with, reactant gas such as SiH₄, SiH₂Cl₂, SiHCl₃, SiCl₄,Si₂H₆, GeH₄, Ge₂H₆, C₂H₂, C₂H₄, or other precursors for semiconductormaterial deposition. The flow rate of the etchant is set such that theetch rate in the selective semiconductor material deposition process isgreater than the deposition rate of a polycrystalline semiconductormaterial on surfaces of the gate electrode 52, the at least one dummygate electrode 53, the gate spacer 56, and the at least one dummy gatespacer 57 and lesser than the deposition rate of a single crystallinesemiconductor material on the sidewalls of the source trench 24 and thedrain trench 26. It is noted that the deposition rate of a singlecrystalline semiconductor material is greater than the deposition rateof a polycrystalline semiconductor material having the same composition.

A first source-side embedded epitaxial semiconductor portion 44A growsfrom the exposed surfaces of the buried single crystalline rare earthoxide layer 20 within the source trench 24 in epitaxial alignment withthe crystal structure of the buried single crystalline rare earth oxidelayer 20. A second source-side embedded epitaxial semiconductor portion44B grows from the sidewall of the first single crystallinesemiconductor material region 32 on the source side in epitaxialalignment with the crystal structure of the first single crystallinesemiconductor material region 32. A third source-side embedded epitaxialsemiconductor portion 44C can grow from a sidewall of a second singlecrystalline semiconductor material region 31 on the source side inepitaxial alignment with that second single crystalline semiconductormaterial region 31. The first source-side embedded epitaxialsemiconductor portion 44A, the second source-side embedded epitaxialsemiconductor portion 44B, and the third source-side embedded epitaxialsemiconductor portion 44C collectively constitute a source-side embeddedsingle crystalline semiconductor material region 44.

If the first single crystalline semiconductor material region 32 and thesecond single crystalline semiconductor material region 31 on the sourceside are epitaxially aligned to the crystal structure of the buriedsingle crystalline rare earth oxide layer 20, the entirety of thesource-side embedded single crystalline semiconductor material region 44is a single crystal. If the first single crystalline semiconductormaterial region 32 and the second single crystalline semiconductormaterial region 31 on the source side are not epitaxially aligned to thecrystal structure of the buried single crystalline rare earth oxidelayer 20, dislocations boundaries can exist among the first source-sideembedded epitaxial semiconductor portion 44A, the second source-sideembedded epitaxial semiconductor portion 44B, and the third source-sideembedded epitaxial semiconductor portion 44C. The dislocation boundariesare indicated with dotted lines in FIG. 4A.

A first drain-side embedded epitaxial semiconductor portion 46A growsfrom the exposed surfaces of the buried single crystalline rare earthoxide layer 20 within the drain trench 26 in epitaxial alignment withthe crystal structure of the buried single crystalline rare earth oxidelayer 20. A second drain-side embedded epitaxial semiconductor portion46B grows from the sidewall of the first single crystallinesemiconductor material region 32 on the drain side in epitaxialalignment with the crystal structure of the first single crystallinesemiconductor material region 32. A third drain-side embedded epitaxialsemiconductor portion 46C can grow from a sidewall of a second singlecrystalline semiconductor material region 31 on the drain side inepitaxial alignment with that second single crystalline semiconductormaterial region 31. The first drain-side embedded epitaxialsemiconductor portion 46A, the second drain-side embedded epitaxialsemiconductor portion 46B, and the third drain-side embedded epitaxialsemiconductor portion 46C collectively constitute a drain-side embeddedsingle crystalline semiconductor material region 36.

If the first single crystalline semiconductor material region 32 and thesecond single crystalline semiconductor material region 31 on the drainside are epitaxially aligned to the crystal structure of the buriedsingle crystalline rare earth oxide layer 20, the entirety of thedrain-side embedded single crystalline semiconductor material region 46is a single crystal. If the first single crystalline semiconductormaterial region 32 and the second single crystalline semiconductormaterial region 31 on the drain side are not epitaxially aligned to thecrystal structure of the buried single crystalline rare earth oxidelayer 20, dislocations boundaries can exist among the first drain-sideembedded epitaxial semiconductor portion 46A, the second drain-sideembedded epitaxial semiconductor portion 46B, and the third drain-sideembedded epitaxial semiconductor portion 46C. The dislocation boundariesare indicated with dotted lines in FIG. 4A.

The semiconductor material of the source-side embedded singlecrystalline semiconductor material region 44 and the drain-side embeddedsingle crystalline semiconductor material region 46 can have the samecomposition throughout. The semiconductor material of the source-sideembedded single crystalline semiconductor material region 44 and thedrain-side embedded single crystalline semiconductor material region 46can be in-situ doped with electrical dopants such as B, Ga, In, P, As,and Sb, or intrinsic. The semiconductor material of the source-sideembedded single crystalline semiconductor material region 44 and thedrain-side embedded single crystalline semiconductor material region 36can be selected from, but is not limited to, silicon, a silicongermanium alloy, a silicon carbon alloy, a silicon germanium carbonally, a III-V compound semiconductor material, a II-VI compoundsemiconductor material, and an alloy or a combination thereof. Thesemiconductor material of the source-side embedded single crystallinesemiconductor material region 44 and the drain-side embedded singlecrystalline semiconductor material region 46 can be the same as, ordifferent from, the semiconductor material of the first singlecrystalline semiconductor material region 32 and the at least one secondsingle crystalline semiconductor material region 31. In one embodiment,the semiconductor material of the source-side embedded singlecrystalline semiconductor material region 44 and the drain-side embeddedsingle crystalline semiconductor material region 46 can be asilicon-germanium alloy or a silicon-carbon alloy, and the semiconductormaterial of the first single crystalline semiconductor material region32 and the at least one second single crystalline semiconductor materialregion 31 can be silicon.

A vertical interface between the second source-side embedded epitaxialsemiconductor portion 44B and the first single crystalline semiconductormaterial region 32 is vertically coincident with a sidewall of the firstsource-side embedded epitaxial semiconductor portion 44A and an outersidewall of the gate spacer 56 on the source side. A vertical interfacebetween the third source-side embedded epitaxial semiconductor portion44C and the second single crystalline semiconductor material portion 31on the source side is vertically coincident with another sidewall of thefirst source-side embedded epitaxial semiconductor portion 44A and anouter sidewall of a dummy gate spacer 57 on the source side.

A vertical interface between the second drain-side embedded epitaxialsemiconductor portion 46B and the first single crystalline semiconductormaterial region 32 is vertically coincident with a sidewall of the firstdrain-side embedded epitaxial semiconductor portion 46A and an outersidewall of the gate spacer 56 on the drain side. A vertical interfacebetween the third drain-side embedded epitaxial semiconductor portion46C and the second single crystalline semiconductor material portion 31on the drain side is vertically coincident with another sidewall of thefirst drain-side embedded epitaxial semiconductor portion 46A and anouter sidewall of a dummy gate spacer 57 on the drain side.

The top surfaces of the first source-side embedded epitaxialsemiconductor portion 44A, the second source-side embedded epitaxialsemiconductor portion 44B, and the third source-side embedded epitaxialsemiconductor portion 44C can be coplanar with, located above, orlocated below, the interface between the gate dielectric 50 and thefirst single crystalline semiconductor material portion 32. Thesource-side embedded single crystalline semiconductor material region 44is a source region of a field effect transistor within the firstexemplary semiconductor structure.

The top surfaces of the first drain-side embedded epitaxialsemiconductor portion 46A, the second drain-side embedded epitaxialsemiconductor portion 46B, and the third drain-side embedded epitaxialsemiconductor portion 46C can be coplanar with, located above, orlocated below, the interface between the gate dielectric 50 and thefirst single crystalline semiconductor material portion 32. Thedrain-side embedded single crystalline semiconductor material region 46is a drain region of the field effect transistor within the firstexemplary semiconductor structure.

If the source-side embedded single crystalline semiconductor materialregion 44 and the drain-side embedded single crystalline semiconductormaterial region 46 are intrinsic or has a dopant concentration less thana target dopant concentration, additional electrical dopants such as B,Ga, In, P, As, and/or Sb can be implanted to increase the dopantconcentration of the electrical dopants in the source-side embeddedsingle crystalline semiconductor material region 44 and the drain-sideembedded single crystalline semiconductor material region 46. In oneembodiment, the dopant concentration in the source-side embedded singlecrystalline semiconductor material region 44 and the drain-side embeddedsingle crystalline semiconductor material region 46 can be from5.0×10¹⁹/cm³ to 2.0×10²¹/cm³, although lesser and greater dopantconcentrations can also be employed.

Referring to FIGS. 5A and 5B, a contact-level dielectric layer 90including a dielectric material is deposited. The contact-leveldielectric layer 90 includes a dielectric material such asorganosilicate glass, silicon nitride, and/or doped or undoped siliconoxide. The contact-level dielectric layer 90 can be deposited, forexample, by chemical vapor deposition (CVD) or spin coating. Thethickness of the contact-level dielectric layer 90 can be from 100 nm to1,000 nm, although lesser and greater thicknesses can also be employed.

Various contact structures are formed within the contact-leveldielectric layer 90 by forming openings within the contact-leveldielectric layer 90, filling the openings with a conductive material,and removing excess conductive material above the top surface of thecontact-level dielectric layer 90. The various contact structures caninclude a source-side contact via structure 94, a drain-side contact viastructure 96, and a gate-side contact via structure 95.

In addition, various metal semiconductor alloy portions can be formed atthe bottom of each opening within the contact-level dielectric layer 90prior to forming the various contact structures (94, 96, 95). Forexample, the various metal semiconductor alloy portions can include asource-side metal semiconductor alloy portion 84, a drain-side metalsemiconductor alloy portion 86, and a gate-side metal semiconductoralloy portion 85. The gate cap dielectric 58 and the at least one dummygate cap dielectric 59 can be removed prior to formation of the variousmetal semiconductor alloy portions (84, 85, 86).

At least one interconnect-level dielectric layer 100 can be formed overthe contact-level dielectric layer 90 and the various contact viastructures (94, 96, 95) embedded therein. Various metal interconnectstructures (104, 106, 105) that are conductively connected to thevarious contact via structures (94, 96, 95) can be formed in the atleast one interconnect-level dielectric layer 100.

The field effect transistor in the first exemplary semiconductorstructure includes a source region, i.e., the source-side embeddedsingle crystalline semiconductor material region 44, which is thickerthan the thickness of the top semiconductor layer 30 and is notsignificantly raised above the top surface of the top semiconductorlayer 30. Further, the field effect transistor in the first exemplarysemiconductor structure includes a drain region, i.e., the drain-sideembedded single crystalline semiconductor material region 46, which isthicker than the thickness of the top semiconductor layer 30 and is notsignificantly raised above the top surface of the top semiconductorlayer 30. The top surfaces of the source-side embedded singlecrystalline semiconductor material region 44 and the drain-side embeddedsingle crystalline semiconductor material region 46 can be coplanarwith, raised above, or recessed below, the interface between the gatedielectric 50 and the first single crystalline semiconductor materialregion 32.

The height of the top surfaces of the source-side embedded singlecrystalline semiconductor material region 44 and the drain-side embeddedsingle crystalline semiconductor material region 46 can be selected tomaintain the parasitic capacitive coupling between the gate electrode 52and each of the source-side embedded single crystalline semiconductormaterial region 44 and the drain-side embedded single crystallinesemiconductor material region 46. In one embodiment, the top surfaces ofthe source-side embedded single crystalline semiconductor materialregion 44 and the drain-side embedded single crystalline semiconductormaterial region 46 can be coplanar with, or recessed below, theinterface between the gate dielectric 50 and the first singlecrystalline semiconductor material region 32. Thus, the parasiticcapacitive coupling in the field effect transistor of the firstexemplary semiconductor structure is not greater than the parasiticcapacitive coupling in a field effect transistor that does not include araised source and drain, while at the same time offering a low sourceresistance and a low drain resistance through the increased thickness ofthe source region and the drain region in the field effect transistor ofthe first exemplary semiconductor structure.

Referring to FIGS. 6A and 6B, a second exemplary semiconductor structureaccording to the second embodiment of the present disclosure can bederived from the first exemplary semiconductor structure of FIGS. 1A and1B by performing the processing steps of FIGS. 2A and 2B without formingany dummy gate stack (51, 53; See FIGS. 2A and 2B) or any dummy gatespacer (57; See FIGS. 2A and 2B).

Referring to FIGS. 7A and 7B, the same processing steps are performed asin FIGS. 3A and 3B in the first embodiment with the modification thatthe edges of the photoresist 77 is laterally shifted to overlie thecontiguous single crystalline semiconductor material region 32′.

Referring to FIGS. 8A and 8B, the processing steps of FIGS. 4A and 4B inthe first embodiment are performed. Alternatively, the processing stepsfor the variation of the first embodiment are performed. A source-sideembedded single crystalline semiconductor material region 44 and adrain-side embedded single crystalline semiconductor material region 46are formed. The difference between the second exemplary semiconductorstructure of FIGS. 8A and 8B and the first exemplary semiconductorstructure of FIGS. 4A and 4B is that a dummy gate electrode and a dummygate spacer do not exist in the second exemplary semiconductorstructure, and therefore, an edge of the source-side embedded singlecrystalline semiconductor material region 44 or an edge of thedrain-side embedded single crystalline semiconductor material region 46are not vertically coincident with any outer sidewall of a dummy gatespacer.

Referring to FIGS. 9A and 9B, the processing steps of FIGS. 5A and 5Bare performed to form a contact-level dielectric layer 90, variouscontact structures (94, 96, 95), various metal semiconductor alloyportions (84, 86, 85), at least one interconnect-level dielectric layer100, and various metal interconnect structures (104, 106, 105).

The field effect transistor in the second exemplary semiconductorstructure includes a source region which is thicker than the thicknessof the top semiconductor layer 30 and is not significantly raised abovethe top surface of the top semiconductor layer 30. Further, the fieldeffect transistor in the first exemplary semiconductor structureincludes a drain region which is thicker than the thickness of the topsemiconductor layer 30 and is not significantly raised above the topsurface of the top semiconductor layer 30. The top surfaces of thesource-side embedded single crystalline semiconductor material region 44and the drain-side embedded single crystalline semiconductor materialregion 46 can be coplanar with, raised above, or recessed below, theinterface between the gate dielectric 50 and the first singlecrystalline semiconductor material region 32. The parasitic capacitivecoupling in the field effect transistor of the second exemplarysemiconductor structure is not greater than the parasitic capacitivecoupling in a field effect transistor that does not include a raisedsource and drain, while at the same time offering a low sourceresistance and a low drain resistance through the increased thickness ofthe source region and the drain region in the field effect transistor ofthe first exemplary semiconductor structure.

While the disclosure has been described in terms of specificembodiments, it is evident in view of the foregoing description thatnumerous alternatives, modifications and variations will be apparent tothose skilled in the art. Accordingly, the disclosure is intended toencompass all such alternatives, modifications and variations which fallwithin the scope and spirit of the disclosure and the following claims.

What is claimed is:
 1. A semiconductor structure comprising: asemiconductor substrate including a buried single crystalline rare earthoxide layer and a trench, said trench having a recessed surface that isrecessed relative to a topmost surface of said buried single crystallinerare earth oxide layer and having sidewalls extending from said topmostsurface to said recessed surface; a single crystalline semiconductormaterial region having a bottommost surface that is in contact with saidtopmost surface of said buried single crystalline rare earth oxidelayer; and an embedded single crystalline semiconductor material regionfilling said trench, wherein a portion of said embedded singlecrystalline semiconductor material region is epitaxially aligned to acrystal structure of said buried single crystalline rare earth oxidelayer, and laterally contacts said single crystalline semiconductormaterial region.
 2. The semiconductor structure of claim 1, wherein asidewall of said trench is vertically coincident with a verticalinterface between said embedded single crystalline semiconductormaterial region and said single crystalline semiconductor materialregion.
 3. The semiconductor structure of claim 2, wherein said verticalinterface is vertically coincident with a bottom portion of an outersidewall of a gate spacer overlying said single crystallinesemiconductor material region.
 4. The semiconductor structure of claim3, wherein said buried single crystalline rare earth oxide layer furtherincludes another trench, said another trench having another recessedsurface that is coplanar with said recessed surface, and saidsemiconductor structure further comprises another embedded singlecrystalline semiconductor material region filling said another trench,epitaxially aligned to said crystal structure of said buried singlecrystalline rare earth oxide layer, and laterally contacting said singlecrystalline semiconductor material region.
 5. The semiconductorstructure of claim 4, further comprising: a gate dielectric contactingan upper surface of said single crystalline semiconductor materialregion; and a gate electrode overlying said gate dielectric.
 6. Thesemiconductor structure of claim 4, wherein said semiconductor structurecomprises a field effect transistor, and said embedded singlecrystalline semiconductor material region or said another embeddedsingle crystalline semiconductor material region serves as a sourceregion of said field effect transistor, and the other of said embeddedsingle crystalline semiconductor material region or said anotherembedded single crystalline semiconductor material region which does notserve as the source region serves as a drain region of said field effecttransistor.
 7. The semiconductor structure of claim 1, furthercomprising a shallow trench isolation structure that contacts saidtopmost surface of said buried single crystalline rare earth oxide layerand laterally surrounds said single crystalline semiconductor materialregion and an upper portion of said embedded single crystallinesemiconductor material region.
 8. The semiconductor structure of claim7, further comprising another single crystalline semiconductor materialportion having a same composition as said single crystallinesemiconductor material portion, laterally spaced from said singlecrystalline semiconductor material portion by said embedded singlecrystalline semiconductor material region, and laterally contacting saidshallow trench isolation structure.
 9. The semiconductor structure ofclaim 8, further comprising a dummy gate stack and a dummy gate spacerlaterally surrounding said dummy gate stack, wherein an interfacebetween said embedded single crystalline semiconductor material portionand said another semiconductor material portion is vertically coincidentwith an outer sidewall of said dummy gate stack.
 10. The semiconductorstructure of claim 1, wherein said single crystalline semiconductormaterial region is not in epitaxial alignment with said crystalstructure of said buried single crystalline rare earth oxide layer. 11.The semiconductor structure of claim 1, wherein said embedded singlecrystalline semiconductor material region includes: a first epitaxialportion that is the same as said portion of said embedded singlecrystalline semiconductor material region; and a second epitaxialportion that is in epitaxial alignment with said single crystallinesemiconductor material region and not in epitaxial alignment with saidfirst epitaxial portion.
 12. The semiconductor structure of claim 1,wherein said buried single crystalline rare earth oxide layer comprisesa single crystalline rare earth oxide selected from Er₂O₃, Gd₂O₃, Nd₂O₃,Pr₂O₃, La₂O₃, and a single crystalline alloy thereof.
 13. Thesemiconductor structure of claim 1, wherein said embedded singlecrystalline semiconductor material region comprises a semiconductormaterial selected from silicon, a silicon germanium alloy, a siliconcarbon alloy, a silicon germanium carbon ally, a III-V compoundsemiconductor material, a II-VI compound semiconductor material, and analloy or a combination thereof.